Steam Boiler Low Pressure

barnic

I hope I'm not breaking any forum rules, but saw that my issue wasn't getting any love any more:
https://forum.heatinghelp.com/discussion/175351/no-pressure-from-steam-boiler-compared-to-last-year#latest

Boiler has lower pressure compared to last year. Ruled out main vents, gas firing rate is correct, no leak in boiler itself (1hr 15min test filled to over top), no leaks at radiator supply valves, no water in gauge assembly.

No air puffing from Gorton main vent like last year (replaced it too). Main vents do get hot. I have one known sagging pipe and its radiator intermittently heats. Could this pipe be condensing so much water that the pressure would not build up?

Any recommended tests to help further troubleshoot or any known ways this can possibly happen?

Thanks for the help!

ethicalpaul

> I have one known sagging pipe and its radiator intermittently heats. Could this pipe be condensing so much water that the pressure would not build up?

Yes. But fill me in on this: Why do you care that your pressure isn't going up? You said your radiators were getting hot to comfortably heat your living space, right?

Jamie Hall

Is there another way to phrase this question? Why was the pressure higher last year? Residential steam boilers don't need pressure to operate -- depending on the size of the system and the piping, a few ounces per square inch to -- at most -- a pound and a half is ample.

So... I would look at it this way: if the system is heating well (except that one problem child) and reasonably evenly, and water consumption is normal (that is very small), it's doing what it's meant to do. So to go back to the top -- why was the pressure higher last year?

barnic

I'm concerned that the boiler may be taking longer to get the radiators filled as either there is a new hole somewhere in the system, or it's not efficiently transferring the heat from burning the gas into the boiler. Both possibilities leading to money up the chimney. The radiators are getting comfortavly hot, but could be talking longer to get hot than they should. It's currently not reading any pressure on the gauge.
Why did it have higher pressure last year? My thinking is either 1. that the steam was restricted only by the vent holes, and pressure rose when the main vents closed and now it's going out another hole. Or 2. The boiler isn't producing the same amount of steam for the same gas rate. Problem 1 I can get my head around, but need help in techniques to find the leak. Problem 2 I'm looking from input from the forum if anyone has ever seen anything like it.

Jamie Hall

Problem 2 is quite possible. Did your annual overhaul include a complete cleaning of the fireside of the boiler and an instrumented adjustment of the burners?

Gary Smith

Check that the pigtail and connection hole from pigtail to boiler is clean, and the pipe path from boiler to low pressure gage is clean. What you have described is exactly how a properly vented one pipe steam system should operate, at very low pressure.

barnic

When I had my hot water heater replaced before the heating season started, I asked if he thought the boiler should be cleaned on the fireside, and he mentioned that there would be very little to clean due to the age of the boiler and the fact that it is gas fired. I'm open to this second opinion of course especially in light of the pressure issue.
As far as cleaning the pigtail assembly. I removed the gauge at "A", and removed the plugs at B, C and D. Some water came out from B and C. Closed B and C, and blew into A, and could feel air at D. Concerning the port at D and its vertical pipe into the boiler, when I filled the boiler above the top, I used this to see the water level. I let the water level get to the green line. When I drained the boiler back to the usual water line, the water left that tube, so I'm assuming its clear unless there is some sort of trap there? Also, I had blown into the gauge, and got the needle to move up.
It has a two stage gas valve, and it has not cycled to the lower stage this season yet. Also the main vent that used to make a huffing noise last year before it closed, is silent now.

Steamhead

@barnic , from what we can see, it sure looks like @EzzyT installed that boiler........

barnic

Actually @Dave0176

Bio

It’s very possible that the previous boiler was oversized thus making more/faster steam per hour for the connected load, steam pressure increases for the same reason, radiators were almost if not fully hot
When a knowledgeable steam guy comes and perfectly sizes your boiler the view is different, you now see 0 to a few ounces of pressure, steam condenses at the radiators and creates a vacuum and more steam enters, only half of the radiator heats up, the vent almost never get hot making them last longer, thermostat is satisfied

Now, on design day, (very few in a year) radiators will
completely get hot and you will see pressure climb up

mikeg2015

That’s not the lowest range gauge you can put on there either. Looks like it goes to 50”. You need a 15” gauge. But even then, if it’s sized well and header and laterals are sized well, there is simply no back pressure and it runs at 1oz or less.

Steam is less dense than air, so it will want to flow to the radiators just by gravity. You only need enough pressure differential to overcome friction in the header and the fall in the header (parallel system). It’s almost like it’s pulled towards the cool metal in a vapor system.